Method of obtaining anisotropic crystalline films and devices for implementation of the method

ABSTRACT

The invention pertains to methods of obtaining anisotropic crystalline films and to devices for carrying out the methods. A colloidal system with anisometric particles is applied as a film onto the surface of a substrate while the viscosity of the colloidal system is lowered. The particles of the colloidal system with lowered viscosity are oriented and the original viscosity of the colloidal system is restored. The film is then dried. The drying is carried out under controlled conditions. Zones of the dried film may be progressively heated to improve the film characteristics.

This application is a 371 of PCT/US02/03800 filed Feb. 6, 2002.

FIELD OF THE INVENTION

This invention relates to a method and device for forming anisotropicfilms on a substrate, and more particularly to methods and devices forforming crystalline films from liquid crystal material for liquidcrystal displays.

BACKGROUND ART

There are various known methods and devices for forming crystallinefilms from various materials. For example, to obtain films ofpolycrystalline silicon one uses a known process of precipitation from agas mixture of silane at low pressure. The process is labor-intensiveand requires expensive equipment to form isotropic polycrystallinefilms.

There are also various known methods of epitaxial growth ofmonocrystalline films, which include gas epitaxy, molecular-beam epitaxyand liquid epitaxy. These processes are technologically labor-intensiveand power consuming, requiring expensive equipment; moreover, there area number of materials for which obtaining anisotropic crystalline filmsis an unsolved problem.

There are known methods of obtaining anisotropic films fromliquid-crystalline (LC) solutions of organic dyes. The methods involveapplication of liquid-crystalline dye solution onto a substrate,application of external orienting action and drying, which providesfilms with optical anisotropy.

There is an increasing requirement to improve the parameters of variousthin film devices and, accordingly, the characteristics and quality offilms used in them. Thus, there is an increase in requirements to thedegree of anisotropy and uniformity of characteristics in filmsfunctioning as polarizing coatings, orienting, phase-shifting,reflecting, brightening and other optical elements as well asanisotropic films for other purposes. It is necessary to create deviceelements based on anisotropic films with an increased degree ofanisotropy, with a more perfect structure, and which do not containadmixtures or structural defects.

SUMMARY OF THE INVENTION

It is a general object of the present invention to provide: 1) animproved crystallization method which allows obtaining anisotropiccrystalline films from colloidal systems (colloid solutions) of variousmatters, 2) a device for implementation of this method, and 3) thincrystalline films obtained with the method and/or device.

The technical result of the invention is the design of the new method ofcrystallization to create anisotropic crystalline films from colloidalsystems of various matters, formed by the anisometric elements of thedispersion phase (kinetic units) distributed in liquid dispersionmedium; simplicity and economy of the method, ensuring high degree ofanisotropy and crystallinity of the obtained films, possibility to formcrystalline films of arbitrary shape (including curvilinear), ecologicalcleanness of the process, low labor-intensity and power consumption.Devices for obtaining anisotropic crystalline films are characterized bythe simplicity of implementation, ecological cleanness, they ensureobtaining films with high degree of anisotropy and good reproducibilityof characteristics.

DESCRIPTION OF PREFERRED EMBODIMENTS

The technical result of the first embodiment is achieved by thefollowing steps: a) application of a layer of the colloidal system withanisometric particles (elements of the dispersion phase) onto thesubstrate, b) external action on the colloidal system to lower itsviscosity, c) external orienting action on the system to providedominating orientation of particles of the colloidal system, d)cessation of the external orienting action or application of additionalexternal action to restore at least the initial viscosity value of thecolloidal system, and e) drying under controlled conditions.

External action on the system to lower its viscosity and externalorienting action on the system to provide dominating orientation ofparticles in the colloidal system can be applied simultaneously withlowering the viscosity or the external orienting action on the systemcan be applied after the process of lowering the viscosity. The externalaction on the system can be implemented via local and/or general heatingof the substrate from the side opposite to that on which the film isformed, and/or local and/or general heating of the substrate and/orlayer from the side of the forming film. Moreover, the heating can beimplemented with electromagnetic (IR, Microwave, etc.) radiation, and/orusing resistive heater, and/or alternating electrical or magnetic field,and/or a flow of heated liquid and/or gas.

External action on the system can also be implemented via mechanicalaction on the layer of the colloidal system applied on the substrate,for example via shearing. Upon the surface of the applied layer ofcolloidal system one directs at least one orienting tool, in thecapacity of which one can use orienting knife-like and/or cylindricalrod, and/or flat plate positioned parallel to the applied layer, and/orat an angle to the surface of the applied layer, at the same time, thedistance from the surface of the substrate to the edge or the plane ofthe orienting tool is set in order to obtain the desired film thickness.The surface of the orienting tool can have a relief. Additionally, theorienting tool can be heated.

Restoration to at least the original value of viscosity of the system isperformed by cession of external action on the system immediately aftercompletion of external orienting action or in the process of externalorienting action.

Drying is preferably performed at humidity no less than 50% and roomtemperature.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more clearly understood from the followingdescription when read in conjunction with the accompanying drawings inwhich:

FIG. 1 is a perspective view schematically illustrating one embodimentof a device for carrying out the present invention.

FIG. 2 is a perspective view schematically illustrating anotherembodiment of a device for carrying out the present invention.

FIG. 3 is a side elevational view schematically illustrating anotherdevice for carrying out the invention including controlled drying.

FIG. 4 is a side elevational view of another embodiment of the deviceshown in FIG. 3.

FIG. 5 is a perspective view schematically illustrating a device forcarrying out the invention including zone processing.

A device for carrying out the method of the first embodiment isschematically illustrated in FIG. 1. The use of this device to fabricatea liquid crystal display is described using a 9.5% aqueous solution ofsulfonated indanthrone, which forms a hexagonal phase at roomtemperature. The dye, utilized in this example, when in solution, formsanisometric supramolecular complexes from molecules of the dye. Thesecomplexes will be the main foundation of the crystalline structure ofthe film. The original ink after purification is deposited onto thesubstrate 1 using dosimeter 2. We have also used such methods ofdeposition as pouring, smearing. They all yield approximately the sameresults in this method.

Further, the colloidal system is impacted so as to lower its viscosity,which is necessary to perform the subsequent crystal alignment. Thesolution forms nematic phase or a mixture of nematic and hexagonalphases. Viscosity of the system is lowered from about 1780 mPa/sec toabout 250 mPa/sec. Quality anisotropic crystalline films have beenobtained when we implemented this preliminary impact to lower viscosityof the system. Optimal implementation of the said external impact is byheating of the deposited layer from the bottom side of the substrateholder, which is carried out via thermal elements 3. The substrateholder is heated so as to raise the temperature of the depositedindanthrone layer to about 56° C. However, good results may also beobtained when heating the deposited layer with electromagnetic radiationor using other methods. A special case of implementation of thedisclosed invention is the use of heated rod 4 to implement locallowering of viscosity of the system with simultaneous alignment of thecrystalline material. The rod may be heated by an additional thermalelement 5.

The next operation is the process of alignment of the kinetic units ofthe colloidal system (LLC). To implement the said external aligningimpact; one may use various aligning tools. In this example we have useda cylindrical Mayer rod wound with a wire, which determined thethickness of the wet layer—9.5 micrometers. When performing the aligningimpact, the rate of translation of the rod was about 13 mm/sec. Shearstress generated by the rod resulted in additional lowering of viscosityof the system.

When alignment was completed, the heating of the substrate holder wasstopped and the heated rod was removed. The film was then dried.Requirements for drying are such that the rate of removal of the solventshould be low in order to prevent disruptions of the previously alignedstructure of the layer. In the above example, drying is performed atroom temperature and humidity 60%. A device for providing controlleddrying will be presently described.

By using this method we obtained anisotropic crystalline films withthickness of 0.3-0.4 micron, with high degree of anisotropy ofparameters: dichroic ratio—Kd=28 with transmission T=40% (whereas withtraditional method of fabrication Kd does not exceed 20), with goodreproducibility of parameters, over the surface of the film, as well asfrom batch to batch. The crystalline structure of obtained films wasevaluated by optical methods and methods of x-ray diffractometry.

A second embodiment of the invention is achieved by the following steps:a) external action on the colloidal system with anisometric particles,situated in a reservoir to lower its viscosity, b) external action onthe system to provide dominant orientation of particles in the colloidalsystem via running it through a slot-die under pressure as the film isapplied to the substrate, c) formation of film with heightened viscosityat the exit from the slot-die due to cessation of the external action orapplication of additional external action to provide restoration of atleast the initial value of viscosity of the colloidal system, and d)drying.

External action on the system can be implemented via heating of thecolloidal system situated in a reservoir. At the same time, the heatingcan be implemented with electromagnetic radiation, and/or resistiveheater, and/or alternating electric or magnetic field, and/or a flow ofheated fluid and/or gas. On the inner walls of a slot-die, externalorienting action is implemented as the film is applied.

After application of layer of the colloidal system onto the substrateone can additionally implement orienting action on the system in thesame direction as in the process of the main orienting action, createdby the relief of the surface of the inner walls of the slot-die. In theprocess of forming crystalline film, the substrate can also be cooled torestore the original viscosity. Drying is preferably conducted athumidity levels of no less than 50% and room temperature.

The colloidal system can use LLC and use external action such as heatingto obtain the phase transition in the system. The colloidal systems maycontain crystalline anisotropic particles. Concentration of thedispersion phase in the colloidal system is chosen such as to providethixotropy of the system. The kinetic units in the colloidal system cancarry a charge.

After restoration of the initial value of viscosity of the colloidalsystem one can implement additional orienting action on the system inthe same direction as in the process of the main orienting action.

A device for carrying out the method of the second embodiment using thesame colloidal solution with the same concentration is schematicallyillustrated in FIG. 2 where like reference numerals have been applied tolike parts. The solution was placed in the reservoir 6 and heated toabout 56° C., which resulted in the phase transition and lowering ofviscosity from the original 1780 mPa/sec to 250 mPa/sec. Alignment wasperformed via extrusion from the slot 7 under the pressure of 1 atmhigher. The gap between the walls of the slot was 50 mm; on one of theinner walls of the slot we formed a relief 8 with step size of 100 mmand height 10 mm. Alignment of LLC was performed in the slot itselfduring extrusion of the colloidal system through the slot. In theprocess of extrusion, the slot is translated over the substrate in sucha way that the extruded layer was uniformly deposited onto thesubstrate. Viscosity in the deposited layer increased up to about 1500mPa/sec due to the phase transition (since heating was only provided inthe reservoir, temperature outside of the reservoir was roomtemperature). Drying operation was performed as described with respectto the first embodiment. The resulting anisotropic crystalline films hadparameters analogous to those obtained in the first embodiment.

We have established that the conditions of drying determine perfectionand peculiarities of the structure in the dried films. Drying conditionslargely determine the degree of their crystallinity. As our experimentshave shown, certain arrangements of the drying process enhance thermalstability of the films. A gradient, created over the substrate, promotesoptimized advancement of the crystallization front, which will largelydetermine dimensions of the crystalline structure of the obtained films,and also will allow eliminating structural defects, which result fromthe orienting influence.

Technical result of the invention is the enhancement of perfection ofthe film's structure, enhancement of reproducibility of film'sparameters over the surface of the film as well as through its thickness(elimination of defects from orienting influence), enhancement ofanisotropy of properties and enhancement of thermal stability of thefilms.

Crystallization of the forming film takes place during the dryingprocess, simultaneously with solvent removal. Therefore, by creatingcertain conditions for removing solvent fumes from the surface of thefilm one can regulate redistribution of solvent molecules inside thefilm, thus affecting crystallinity of its structure.

We have established that to perfect the film's structure, enhance degreeof anisotropy and reproducibility of film's properties, it is necessaryto provide conditions where removing the solvent happens slowly without(or with minimal) convection over the film's surface. Thus, arrangedforced slowing of the drying rate, i.e. the quantity of solventmolecules leaving the film per unit of surface area per unit time, keepssolvent molecules in the film and slows the rate of their redistributioninside the films towards the surface. This slows the rate ofcrystallization and creates favorable conditions for aligninganisometric particles in the certain predetermined direction.Redistribution also takes place in the structure of the anisometricparticles, which also favorably affects perfection of the crystallinestructure of the forming film.

By the term finite volume in this case we mean the volume above thesurface of the forming film, which is confined by a shell or a lid,where there are openings (slot, porous membrane, sliding panel of ashell and other), dimensions of which are such that the rate ofdeflecting the fumes is less than it would be if the process wereperformed in an infinite volume. By the term infinite volume we meansufficiently large volume when an increase or a decrease of this volumeover the surface of the forming film would not affect the rate ofdeflecting solvent fumes, i.e. the drying rate.

Therefore, the limiting stage of the drying process in the disclosedmethod is the rate and the direction of deflecting solvent fumes fromthe surface of the substrate. The process takes place according todiffusion kinetics, which creates more “calm” conditions for formingcrystalline structure.

Since the process of removing the solvent is usually accompanied bysignificant change of geometric dimensions (thickness) and surfacemorphology of the film, by creating conditions to slow down thedirectional displacement of the solvent we thus create conditions formore gradual redistribution of solvent molecules in the film and moreuniform and organized additional structuring of anisometric particles ofthe system (already after their external orientation) during dryingprocess. This leads to lowering elastic stresses during crystallizationprocess, which are due to geometrical deformation of the film. As aresult, this enhances perfection of the film's structure and degree ofits anisotropy.

By limiting the volume over the crystallizing film, we create conditionsto increase solvent vapor pressure above the forming film, so that theeffective solvent evaporation rate drops.

We use the term finite volume—when changing the volume affects the rateof removing molecules of an arbitrary material (in our case it is thesolvent), i.e. the rate of drying. If the volume of a shell or achamber, where the drying process takes place, will be sufficientlylarge, then changing it would not be noticeably reflected in the dryingrate.

We have established experimentally that the mentioned technical resultis achieved by the fact that in the process of forming crystallineanisotropic films from colloidal systems with anisometric particles,which includes application of the colloidal system onto the substrateand in situ and/or subsequent orienting influence and drying, the dryingoperation is performed at a temperature in the interval from 0° to 50°C. and humidity in the interval from 60 to 90% with forced drying rateslowing via performing the drying process in a finite volume, which isselected with the condition to restrict deflection of solvent fumes fromthe surface of the forming film.

Moreover, the finite volume over the surface of the forming film may becreated by performing the drying process in a shell covering at least apart of the surface of the wet film.

FIGS. 3 and 4 illustrate devices for drying in accordance with thisembodiment of the invention. A liquid crystal solution 9 is fed from thereservoir 10 through the channel 11 onto substrate 12. The channel 11has a traverse dimension so as to cover the entire width of filmformation. The rate of feed of the solution from the reservoir 10 andthe relative speed of translation of the reservoir and the feedingchannel relative to the substrate 12 is determined by the desiredthickness of the layer or film. Alignment of the supramolecularcomplexes in the layer of LC is preformed with Mayer rod 13 (metallicrod wound with a wire) by application of shear stress. The substratewith the deposited anisotropic film is then subjected to the dryingoperation (removal of the solvent from the layer of LC). Drying isperformed in enclosure 14 in which the required conditions oftemperature and humidity above the surface of the film are established.FIG. 3 shows the enclosure 14 covered by a semi-permeable membrane 15,which provides certain retardation of the drying process. In thisexample, with the pore diameter of about 15 nm and constant temperatureof 18° C. inside the enclosure, the humidity above the surface of thefilm was about 90%. To control conditions of the ambient medium duringthe process, the enclosure is equipped with humidity sensors 16 andtemperature sensor 17. All the mentioned elements: enclosure 14,substrate 12, rod 13, and reservoir 10 and channel 11 have means forrelative translation (not shown). All operations according to thedisclosed invention may be combined in a single in-line process. In thiscase, all the elements mentioned above are mounted on a single frame 18.Operation of the system to form the film is as described with respect toFIGS. 1 and 2.

Another method of implementing forced slowing of the drying process isto make the enclosure with a lid 19 featuring a movable slit 20, FIG. 4.Dimensions of the slit and its speed of translation should correspond tothe condition of creating the required parameters of temperature andhumidity above the surface of the film.

For different examples, we have obtained results, which show theinfluence of conditions of drying on the structure and properties offorming films. However in all examples, the index of degree ofanisotropy of films, perfection of the structure of films,reproducibility of parameters of films over the area and throughouttheir thickness, as well as thermostability of films is significantlyhigher than analogous indexes obtained with regular drying conditions inair at room temperature (for comparison we used films obtained withidentical conditions of deposition and alignment).

The following is an example of forming an anisotropic film from LLC ofindanthrone. An eight percent weight aqueous LC solution of sulfonatedindanthrone was deposited onto glass substrate via the known method(with external aligning influence on the colloidal system). In thissolution, molecules are packed into stacks comprising supramolecularcomplexes, which are the anisometric particles of the system. When theLC solution is being aligned, these complexes are oriented along thedirection of the aligning influence. Thickness of the film before dryingwas 5-10 μm. The sample was dried in various conditions: a) in air, ininfinite volume at room temperature, b) in air, in infinite volume attemperature 10-15° C., c) in air, in a finite volume at temperature 20°C. The enclosure was 15 mm away from the surface of the forming filmwith a porous membrane 15 with pore diameter 10-20 nm sitiated above thefilm for slowed removal of solvent vapors from the volume of theenclosure and to create humidity gradient along the normal to thesurface of the film. In another experiment, in a finite volume attemperature 20° C. created by the enclosure with lid 19 with its edgetranslating at the rate of 0.1-1 cm/min over the surface of the formingfilm, and therefore creating tangential humidity gradient, wherein thedirection of translation is such that propagation of the crystallizationfront is parallel to the direction of the aligning influence duringformation. An analogous experiment was carried out with the direction oftranslation of the edge of the enclosure perpendicular to the directionof the aligning influence during formation.

Comparative analysis of the obtained films showed that implementing thedisclosed method enhances optical characteristics of films by 15-30%compared to films obtained with “traditional” methods. Besides that,these methods “heal” the technological macro-defects: streaks and tracesof the depositing and aligning tools (rod). As evident from x-rayinvestigations the films themselves also have more perfect crystallinestructures. Increased thermal stability by about 10% is alsocharacteristic of films that have been dried in the finite volume.

Additional results are obtained when using micro-porous membrane in thecapacity of the substrate, additional translation of the thermal zoneover the surface of the substrate, as well as implementation ofautomated operation of processes of formation of the film and controlover the drying process itself and directly the process of formation ofthe film.

Usually, one uses porous membrane 15 with pore diameter from 4 nm to 2mm and porosity no less than 5%. Porosity is selected such as to providea diffusion barrier to control the flow of gas (solvent). If it isnecessary to perform accelerated drying while providing good results,one may use membrane with pore diameter on the order of 0.1 mm.

If one uses micro porous membrane for the substrate on which thecolloidal system is deposited as a layer, removal of the solvent willtake place through both surfaces of the forming film. Furthermore,parameters of the external membrane and the membrane of the substratemay be selected such that they will create the most identical conditionsof removing the solvent, which would yield an even more perfectstructure in the film. Usually, the size of pores in the internal andthe external membranes are selected equal, or the pore size in theexternal membrane is chosen somewhat larger than in the internal one.Porosity of membranes is chosen different by depending on the necessaryrate of solvent fumes removal. Optimally, porosity and membranethickness are chosen such as to provide slowing of the drying process noless than by 1.5 times compared to the rate of drying in analogousconditions, but without slowing of the solvent fume deflection rate.

Drying of the forming film may be performed at a temperature less thanthe temperature of deposition and/or orientation of the colloidalsystem, or at a temperature equal to the temperature of depositionand/or orientation of the colloidal system, or at a temperature higherthan the temperature of deposition and/or orientation of the colloidalsystem. Drying of the forming film may be performed at humidity higher,equal or less than the one during deposition and/or orientation of thecolloidal system.

In the disclosed method, the drying operation may also be performed inat least two stages, first of which is performed at temperature lowerthan the temperature of deposition and/or orientation of the colloidalsystem and humidity higher than the one during deposition and/ororientation of the colloidal system, but the last stage is performed attemperature and humidity which are equal to the ones that were usedduring deposition and/or orientation of the colloidal system.

Drying may be performed in air medium or in the medium of an inert gas,or in chemically active medium, which provides modification ofproperties of the forming film. To create the necessary medium, thesubstrate holder with the forming film on it together with the devicerestricting the rate of deflecting solvent fumes (shell with a slot or amembrane), are placed in an additional casing or reactor.

Usually, drying is carried on until the solvent content in the formingfilm is from 5% to 15 %. Additionally, after completing the dryingprocess, the formed film may be aged at temperature from 60° to 150° andnormal humidity. After that, a protective layer may be formed on it.

Drying may also be performed in the presence of temperature gradientprovided by at least a single directed translation of the temperaturezone over the surface of the forming film. Here, the direction oftranslation of the temperature zone is chosen at an angle from 0° to180° to the direction of external orienting influence. Temperature zonemay be moved over the film's surface two or more times. Then, directionof each subsequent translation is chosen to be at an angle from 0° to90° to the previous one.

In the process of drying and/or after completion of the drying process,one may perform a single aging, of the forming or already formed film,at humidity level higher than that during the drying process. Afterthat, one performs additional drying of the forming film. Such cyclicrepetition of operations allows smoothing out stress effects on thecrystal structure of the forming film introduced during fabrication.

We have found that additional thermal processing of the film obtainedaccording to the invention leads to not only ablation of any unwantedadmixtures, but also to enhanced characteristics of the film andenhanced degree of anisotropy. Additionally, we observed an increase indegree of crystallinity in the film, and enlargement of thesupramolecular complexes themselves, which form the structure of thefilm. We have also found an increase in the thermal stability of thefilm. These results are achieved by thermal processing of the film orlayer by a directional translation of a temperature zone along thesubstrate surface.

An example of a device for carrying out the zone heating is illustratedin FIG. 5. As an example, let us consider obtaining anisotropicpolarizing film from aqueous liquid crystal solution of sulfonatedindanthrone. To obtain the liquid crystal we used 3.0 g. of sulfonateddye, free from inorganic salts, which is dissolved while heated in 37 mlof solvent (H₂O). Then, solution is cooled to room temperature. Presenceof liquid crystal phase is registered when the sample is observed underpolarizing microscope equipped with two crossed polarizers.

The liquid solution is fed under pressure from the reservoir 21 throughthe channel 22 onto the glass substrate 23. The LC solution is depositedonto the glass substrate with dimension 100×100 mm² at room temperatureand humidity 70%, so as to obtain a film of LC with dimensions 80×80mm². The rod 24 in the form of rotating cylinder with diameter—20 mm andlength—200 mm is placed above the flat surface of the substrate withoutpossibility to move along it, but with possibility to rotate around itsown axis. On the edges of the cylinder there are spacers 25, which are10 μm thick and 5 mm wide. It is these spacers that determine thethickness of the film. Stage 26 with the substrate 23 is translated at20 mm/sec relative to the stationary rotating cylinder so that thecylinder in effect is rolling on the surface of the substrate. In thisprocess, liquid crystal of the dye is uniformly distributed over thesurface of the substrate and the supramolecular complexes are aligned inthe layer of LC. Until the moment of complete drying of the film, it isplaced in the enclosure 27, which is built so that it hinders theevaporation of the solvent from the layer of LC, as described above.

A heating element 28, which creates a zone of elevated temperature inthe layer of LC (about 450° C.), is translated above the surface of LClayer. The direction of translation of the thermal zone can be chosen tocoincide with the direction of, or be perpendicular to, the externalinfluence. Thermal influence is performed in conditions of elevatedhumidity (95%) in order to prevent complete drying of the film.

The speed of translation of the thermal zone is set to obtain uniformheating throughout the thickness of the film as it is formed. The speedof translation of the thermal zone is from 0.5 to 10 mm/sec. To create asharper border of the thermal zone one may use additionally mountablescreens.

As the result, we obtain anisotropic films, having the followingcharacteristics: T₀=45%, D_(⊥)/D_(∥)=22 compared to D₁₉₅ /D₈₁ =16.5 forfilms obtained with traditional methods without additional thermalprocessing.

To implement the disclosed invention one may use also other methods. Forexample: on the stage of the external aligning influence one may use aheated Mayer rod, or translate a heated wire under the substrate.

During implementation of the disclosed method, it is preferred tocontrol all technological parameters of the process. Furthermore,manipulation of operations may be automated. One may use liquid crystalsolution of an organic dye, where solution concentration determines thepresence of anisometric particles—supramolecular complexes in solution.In an LLC, one may use at least one organic dye containing in itsstructural formula at least one ionogenic group providing its solubilityin polar solvents in order to form lyotropic liquid crystal phase,and/or at least one anti-ion, both of which in the process of formingoptically anisotropic film either remain in the structure of a moleculeor not.

In order to obtain anisotropic films one may use various organicmaterials, which form colloidal system with anisometric particles.Molecules of the listed below materials have flat shape and whendissolved in a suitable solvent (usually just one) they formsupramolecular complexes, which are the anisometric particles of thecolloidal system. Based on LLC of the mentioned materials (which will bethe very colloidal systems) one may obtain films with opticalanisotropy. The following are examples of such organic materials:

-   -   Dyestuffs (Translator: in the original text Color Indices and        some other additional information are absent; all these data are        added to make the information more accurate):    -   polyrmethine dyestuffs, for example, “pseudoisocyanine”,        “pinacyanol”; triarylmethane dyes, for example “osnovnoi        biriuzovii” (C.I. Basic Dye, 42035 (Turquoise Blue BB (By))),        “kislotnii yarko-goluboi 3” (C.I. Acid Blue 1, 4204);    -   diaminoxanthene dyes, for example, “sulforhodamine S” (C.I. Acid        Red 52, 45100 (Sulforhodamine B));    -   acridine dyes, for example, “osnovnoi zholtii K” (C.I. Basic        Dye, 46025 (Acridine Yellow G and T(L)));    -   sulfonation products of acridine dyes, for example, of        “trans-quinacridone” (C.I. Pigment Violet 19, 46500        (trans-Quinacridone));    -   water-soluble derivatives of anthraquinone dyes, for example,        “aktivnii yarko-goluboi KH” (C.I. Reactiv Blue 4, 61205);    -   sulfonation products of vat dyes, for example, of “flavantrone”        (C.I. Vat Yellow 1, 70600 (Flavanthrone), of “indantrenovii        zholtii” (C.I. Vat Yellow 28, 69000), of “kubovii zholtii 4K”        (C.I. Vat Orange 11, 70805), of “kubovii tyomno-zelenii Zh”        (C.I. Vat Green 3, 69500), of “kubovii fioletovii S” (C.I. Vat        Violet 13, 68700), of indanthrone (C.I. Vat Blue 4, 69800        (Indanthrone)), of perylene violet dye (CAS: 55034-81-6), of        “kubovii alyi 2Z” (C.I. Vat Red 14, 71110);    -   azo-dyes, for example, Benzopurpurine 4B (C.I. Direct Red 2,        23500), “Pryamoy zheltii svetoprochniy O”, “Pryamoy zheltii        svetoprochniy” (C.I. Direct Yellow 28, 19555);    -   water soluble diazine dyes, for example, “Kislotnii        temno-goluboi Z” (C.I. Acid Blue 102, 50320);    -   sulfonation products of dioxazine dyes, for example, of “pigment        fioletovii dioxazinovii” (C.I. Pigment Violet 23, 51319);    -   water-soluble thiazine dyes, for example, C.I. Basic Blue 9,        52015 (Methylene Blue);    -   water-soluble derivatives of phtalocyanine dyes, for example,        cupric octacarboxyphtalocyanine salts;    -   fluorescent bleaches,        as well as other organic materials, for example,        disodium-chromeglycate etc., and inorganic materials capable of        forming colloidal system with anisometric particles.

In the capacity of the colloidal system one may also use systems createdfrom inorganic lyotropic liquid crystals, such as iron oxohydroxide orvanadium oxide and others.

There has been described a method of obtaining thin anisotropiccrystalline films includes application of colloidal system withanisometric particles, or macromolecules, or supra-molecular complexes,which are formed by the grouped and oriented in some way moleculesexisting in pre-crystalline state onto the substrate. It is preferredthat the degree of anisotropy (the ratio of the length to the thickness)of kinetic units of the colloidal system are no less than 10. Colloidalsystem should also exhibit thixotropy. For this purpose, colloidalsystem should exist at a certain temperature and have certainconcentration of the dispersion phase. The colloidal system (or paste)is brought into the state of heightened fluidity via any type ofexternal action, which loweres viscosity of the system. This could beheating, deformation, etc. External action can continue during theentire next process of orientation or take the time necessary in orderthat the system does not relax into the state with heightened viscosityduring the orientation time.

The next operation of the method is the external orienting action on thesystem, which could be implemented as by mechanical as well as any othermethod. The degree of mentioned action should be sufficient so thatkinetic units of the colloidal system obtain the desired orientation andform the structure, which will be the foundation of the future crystallattice in the obtained film. Operations of rendering the colloidalsystem into fluid state and external orienting action on it can bejoined in time and performed sequentially on various regions of thefilm.

The next operation of the declared method is rendering of the orientedarea of the obtained film from the state with lowered viscosity, whichwas achieved by the first external action, into the state with theinitial or higher viscosity. This is implemented so as to avoiddisorientation of the structure and creating defects on the surface ofthe film. This operation is necessary and cannot be implemented as justa process of free or forced drying, i.e. removing the solvent from theformed film. Before the drying process, viscosity of the system shouldbe raised either by removing the earlier applied action, which providedlowering of the viscosity before the orienting process, or by anadditional forced action on the system to “freeze” its structure. Onlythixotropic colloidal systems, when exerted with the above actions canensure obtaining the desired results at each of the above-listedintermediate stages of forming anisotropic crystalline films.

The final operation of the declared method is the drying operation(solvent removal), in the process of which the crystalline structure inthe obtained film is formed. Regimes of drying operation should bechosen so as to eliminate the possibility of disorientation of theearlier obtained structure and provide relaxation of stresses(“smoothing” of the crystalline lattice defects) appearing duringexternal orienting action. It is preferred to perform drying process atraised humidity (no less than 50% at room temperature). The criticalfactor for obtaining high degree of crystallinity in the obtained filmwill be the speed and directionality of the solvent removal out of thesystem.

1. A method of fabricating anisotropic crystalline films comprising thesteps of: applying a layer of a colloidal system with anisometricparticles onto a substrate, externally impacting the colloidal system tolower the viscosity of the applied layer of the colloidal system,applying external orienting action on the colloidal system to providedominant orientation of particles of the colloidal system, allowing thedeposited colloidal system with dominant orientation of the particles toreturn to at least its initial value of viscosity, and drying thedeposited layer.
 2. The method according to claim 1 wherein the externalimpact on the colloidal system and the external orienting action on thesystem are carried out simultaneously.
 3. The method according to claim1 wherein the external impact on the colloidal system further comprisesheating the colloidal system to lower its viscosity prior to applyingthe external orienting action.
 4. The method according to claim 2wherein the external impact on the system is performed via mechanicalaction on the layer of colloidal system as it is applied onto thesubstrate.
 5. The method according to claim 1 wherein during the dryingof the deposited layer, humidity gradients are created in tangential ornormal direction above the surface of layer.
 6. The method according toclaim 5 wherein the finite volume over the surface of the depositedlayer is created by performing the drying operation in a shell encasingat least a part of the surface of the layer and humidity gradient abovethe surface of the deposited layer is created via at least a singleshifting of the shell along the surface of layer in at least onedirection.
 7. The method according to claim 1 wherein the drying of thedeposited layer is performed at a temperature in the interval 0° to 50°C. and humidity in the interval from 60 to 90% with a forced slowing ofthe drying rate by performing the process in a finite volume which isconfigured to resist deflection of solvent fumes from the surface of thedeposited layer.
 8. The method according to any of claim 1 or 7, whichfurther comprises a thermally processing the deposited layer via atleast a single directional pass of the temperature zone along the layer.9. The method according to claim 8, wherein the temperature zone iscreated via a local heating of the substrate on the side opposite tothat on which the deposited layer is formed.
 10. The method according toclaim 8, wherein simultaneously with the local heating in thetemperature zone, the rest of the substrate is cooled.
 11. The methodaccording to claim 8, wherein the temperature of the temperature zone ischosen to be no less than 10% higher than the substrate temperature andno less than 10° less than the decomposition temperature of thecrystalline film.
 12. The method according to claim 8, wherein thedirection of pass of the temperature zone is chosen to coincide with thedirection of the orientation.
 13. The method according to claim 8,wherein the multiple passes of the temperature zone are performed withthe direction of each subsequent pass chosen at an angle from 0° to 180°to the previous one.
 14. The method according to claim 8 wherein for atleast a part of the time during fabricating of the anisotropiccrystalline film the deposited layer is under constant electric and/ormagnetic field.
 15. The method according to claim 7 wherein the finitevolume is created by a shell, at least part of which is implemented inthe form of porous membrane having pore diameter from 4 nm to 2 mm andporosity no less than 5%.
 16. The method according to claim 7 whereinthe drying step is performed at a temperature lower than the temperatureof deposition and orientation of the colloidal system, and humidityhigher than the humidity of deposition and orientation of the colloidalsystem.
 17. The method according to claim 7 wherein a microporousmembrane is used as the substrate for the application of the colloidalsystem.
 18. The method according to claim 7 wherein the drying isperformed until a solvent content in the film is 2 to 15%.
 19. Themethod according to claim 7 wherein, after completion of the drying, thecrystalline film is aged at temperature from 60° to 150° and normalhumidity.
 20. A method of fabricating anisotropic crystalline filmscomprising the steps of: external impacting a colloidal system withanisometric particles situated in a reservoir to lower the viscosity,external orienting action on the colloidal system to provide a dominantorientation of particles of the colloidal system via running it througha slot-die under pressure, formation of a film with raised viscosityupon exiting from the the slot-die due to cession of the external impactor application of an additional external impact to provide restorationof at least the initial value of viscosity of the colloid system,application of the said formed film onto a substrate, and drying thedeposited layer.
 21. The method according to claim 20 wherein theexternal impact on the colloidal system is performed via heating thecolloid system placed in the reservoir.
 22. The method according toclaim 20 wherein the external orienting action is performed using theslot-die, inner walls of which feature the orienting relief.
 23. Themethod according to claim 20 wherein a lyotropic liquid crystal is usedin the capacity of the colloid system.
 24. The method according to claim20 wherein the external action is chosen such as to ensure phasetransition in the colloid system.
 25. The methods according to claim 20wherein sol or gel is used in the capacity of the colloid system. 26.The method according to claim 20 wherein the anisometric particles inthe colloid system are crystalline.
 27. The method according to claim 20wherein one uses the colloid system, concentration of dispersion phasein which is chosen such as to provide thixotropy of the system.
 28. Themethod according to claim 20 wherein the anisometric particles in thesystem carry charge.
 29. A device for fabricating a crystalline film ona substrate comprising: a substrate holder, means mounted on a selecteddistance above the substrate for applying a layer of a colloidal systemwith anisotropic particles of predetermined thickness onto the substratecarried by the substrate holder, an orienting tool for applying anorienting action on the colloidal system applied to the substrate, andmeans for heating the colloidal system applied to the substrate.
 30. Thedevice according to claim 29 wherein the means for heating the colloidalsystem heats at least part of the substrate holder.
 31. A device forfabricating a crystalline film on a substrate comprising: a reservoirfor placing a colloid system, supplied with heating elements and meansof creating extra pressure in a reservoir, a substrate holder, installedat a controlled distance under the reservoir with possibility ofmovement relative to the reservoir in the horizontal plane; wherein thelower part of the reservoir has an opening in the shape of a slot-die,dictating conditions of an orienting impact.
 32. The device according toclaim 31 wherein under the substrate holder there is a thermo-elementimplemented such that it allows maintaining certain temperature over atleast a part of the substrate holder surface.
 33. The device accordingto claim 31 wherein at least a part of the slot-die surface features arelief.
 34. The device according to claim 31 wherein at least a part ofthe slot-die surface features hydrophilic or hydrophobic coating.